docs: def sphere_pos(self, x):
          """Sphere (squared norm) test objective function"""
          # return np.random.rand(1)[0]**0 * sum(x**2) + 1 * np.random.rand(1)[0]
          c = 0.0
          if x[0] < c:
              return np.nan
          return -c**2 + sum((x + 0)**2)